There are number of different potential, handoffs that can occur for a MS. These include, as non-limiting examples, inter-PDSN (Packet Data Service Node) handoffs, inter-BS (Base Station) hard handoffs, inter-BS soft handoffs, and inter-PCF (Packet Control Function) hard handoffs. In each of these different types of handoffs a problem that arises is related to preserving the context of the connection with the MS during the transfer. This invention is directed towards solving the context transfer problems that arise in the inter-PDSN handoff case. Commonly assigned U.S. patent application Ser. No. 10/878,455, filed on even date herewith and entitled “Method and Apparatus Providing Context Transfer for Inter-BS and Inter-PCF Handoffs in a Wireless Communication System”, by Sarvesh Asthana and Jianhao Michael Yang, is directed towards solving the context transfer problems that arise in the inter-BS and inter-PCF handoff scenarios, and may thus be considered a related application to this patent application, and is incorporated by reference herein in its entirety.
Internet Protocol (IP) applications in the mobile network require mobility management to maintain session continuity. Mobility management at the IP layer currently depends on the Mobile Ipv4 or Mobile Ipv6 (Mobile IP Version 4, Mobile IP Version 6) specifications. Mobile IP allows an application to maintain the same IP address as it moves from one network/link to another. Thus, the use of Mobile IP obviates the need to re-establish a session whenever the MS moves from one network to another.
However, a Mobile IP handover involves link layer and IP layer signaling, and during this signaling phase the MS cannot send or receive data packets. The resulting delays in packet transmission and/or reception can be large with high latency links, and are generally unacceptable for real-time services where packet loss is very visible to the end-user. Seamless mobility management techniques are generally required for such services.
Seamless mobility management is intended to eliminate service interruption and to reduce packet loss and delay time, and thus increase the quality of service (QoS). The seamless handoff can be achieved through a fast handoff and context transfer.
Generic fast handoff mechanisms can reduce the IP layer signaling delays, and some progress has been made in this area. Generic context transfer protocol has also been proposed. However, there are at two issues that are not yet addressed for the existing context transfer mechanisms. A first issue concerns contexts for real time applications such as VoIP (Voice over Internet Protocol), where time sensitivity of the context transfer is critical. Considerable care must be given to when to transfer these contexts, and how to maintain the accuracy of the contexts during the transfer. A second issue involves the distinction between link layer contexts and IP layer or application contexts. The link layer context is technology-specific, and is normally coupled together with the handoff mechanism for the particular wireless technology. For example, it is the case in a Code Division Multiple Access (CDMA) wireless technology (e.g., CDMA 2000 1x networks) that when the MS performs an inter-PDSN handoff, there are four types of contexts that can be transferred.    1. The first context is a PPP (Point to Point Protocol) context. These are the time insensitive PPP parameters the MS originally negotiated with an anchor PDSN. In this description the anchor PDSN is considered to be the PDSN where the current PPP link is terminated, as contrasted with a Target PDSN, which is the PDSN to which the MS is moving, and that will provide future service for the MS. The PPP context transfer is possible for Mobile IP because the PPP negotiation process does not involve an IP address assignment to the MS, and no authentication between the PDSN and the MS is required. As the parameters exchanged during PPP negotiation are static, time-insensitive parameters there is no need to re-negotiate the PPP session when the PPP end point switches to the target PDSN. The PPP context can be transferred in multiple messages in a way to simulate the PPP negotiation, since the PPP stack is state aware.    2. The second context is the IP layer QoS parameters, such as the Traffic Flow Template (TFT).    3. The third context is Header compression state information, such as ROHC (Robust Header Compression) states.    4. The fourth context of interest is the link layer context in the anchor BS (Base Station). Such context can be the SR_ID, service option configuration, and link layer assisted header compression information. For example, the link layer context can include the state information for LLA-ROHC (Link Layer Assisted-ROHC).
The latter two types of context are time sensitive, meaning that they should be kept updated in order to ensure accuracy.
The following published standards and other documents are related to this invention: 3GPP2 TSG X.P0011.3: Wireless IP Network Standard: Packet Data Mobility and Resource Management; 3GPP2 TSG X.P0011.2: Wireless IP Network Standard: Simple IP and Mobile IP Access Services; 3GPP2 TSG A.S0013-A v2.0.1: 3GPP2 IOP for CDMA2000 Access Network Interface; “Fast Handovers for Mobile IPv6”, IETF [mobile-ip] Working Group draft, Rajeev Koodli (Ed.), Jan. 30, 2004; “Fast Handovers and Context Transfers in Mobile Networks”, Rajeev Koodli and Charles E. Perkins, Computer Communication Review, a publication of ACM SIGCOMM, volume 31, number 5, October 2001. ISSN # 0146-4833; and RFC3220: IP Mobility Support for IPv4, C. Perkins (Ed.) January 2002.
When a MS is roaming from a BS to another BS, where the new BS cannot reach the serving PDSN, the Mobile IP handoff occurs. In this case the MS needs to obtain a new IP address, maintain the state information for the connection configuration or applications, and update the corresponding node with the new information so that the active service interruption is minimal. However, a conventional generic context transfer mechanism (see again “Fast Handovers and Context Transfers in Mobile Networks”, Rajeev Koodli and Charles E. Perkins, ACM SIGCOMM, volume 31, number 5, October 2001) does not address the need to distinguish different types of contexts as to when to transfer context, and how to keep the context updated.
For example, a handoff for VoIP from one PDSN to another PDSN would require the system to transfer the following contexts: PPP context, HRL (Header Reduction Lower) context, HRU (Header Reduction Upper) context and the QoS context, such as the TFT and SR_ID.
A loss of these contexts during the handoff will result in a loss of the QoS and will require a re-negotiation of the QoS. There can be additional delays caused due to re-establishing the contexts (e.g., for QoS or Header compression). These delays can be particularly long when roaming to a slow access network (a high latency link). The seamless handoff also needs to transfer the context at the correct time, and to the correct location.
The P-P interface as defined in 3GPP2 is one attempt to minimize the delay and maintain the contexts when the MS roams from one PDSN to another. This approach creates a tunnel between the anchor PDSN and the target PDSN, when the MS is moving from the anchor PDSN to the target PDSN, and data frames are tunneled through the target PDSN to the anchor PDSN. Packet loss is minimized to the period when the MS performs the actual physical layer switching. Contexts that are maintained by the PDSN are not required to be transferred since, effectively, the serving PDSN is not changed after the handoff. However, this approach has a number of drawbacks.
In the sense of RFC3220 a tunnel is considered to be a path followed by a datagram while it is encapsulated. This model assumes that while it is encapsulated, the datagram is routed to a knowledgeable decapsulation agent, which decapsulates the datagram and then correctly delivers it to its ultimate destination. In this model the PDSNs are considered to be knowledgeable decapsulation agents.
A first drawback of the conventional approach is an increase in the burden on the PDSN, as each service instance for a MS will have one P-P session between the anchor PDSN and the target PDSN for the duration of an active application session. This situation can consume a considerable amount of network resources (e.g., the PDSN memory, processing power, and the bandwidth of the links between the PDSNs).
A second drawback of this approach is an inefficient use of network resources. For example, during a data session each GRE (Generic Routing Encapsulation) packet contains a RLP (Radio Link Protocol) frame which can be in excess of 30 bytes. A large number of small packets are generated and communicated among the IP core network, which does not occur if the P-P interface is disconnected.
A third drawback relates to the required “triangle routing”, where IP packets pass through an additional hop between the anchor PDSN and the target PDSN. Ideally, the P-P interface should be released as soon as possible, if such release does not interrupt the application service.
A fourth drawback is that the conventional technique does not actually use the concept of the Mobile IP fast handoff, because the MS does not perform Mobile IP registration for the lifetime of the active connection. The P-P interface procedure therefore cannot be used for an inter-technology handoff.
The generic context transfer mechanism (see again “Fast Handovers and Context Transfers in Mobile Networks”, Rajeev Koodli and Charles E. Perkins) does not distinguish between the static and dynamic natures of contexts. It also does not address the use of link layer contexts to reduce link layer setup delay.
It should thus be apparent that there is a need to provide an improved technique for performing inter-PDSN type of handoffs. Prior to this invention, this need was not adequately addressed or fulfilled.